1. Field of the Invention
The present invention generally relates to a paper feeding mechanism, and more particularly to a paper feeding mechanism applied in an automatic document feeder.
2. The Related Art
A conventional paper feeding mechanism applied in an automatic document feeder includes a mechanical frame, an input tray, a drive assembly and a pickup assembly. The input tray is assembled to the mechanical frame. The drive assembly is mounted to the mechanical frame. The pickup assembly is driven by the drive assembly and is assembled to the mechanical frame and located above the input tray. After a stack of paper is placed on the input tray, the drive assembly drives the input tray to be raised up to a constant height according to a thickness of the stack of paper placed on the input tray, and then the pickup assembly starts picking up the paper.
However, after the pickup assembly picking up the paper for a while, the thickness of the stack of paper becomes thinner and the height of the input tray keeps constant that weakens a picking up strength of the pickup assembly exerted on the paper and even makes the pickup assembly unable to pick up the paper.